Preparation of 2,2-bis-hydroxymethyl-butanediol-(1,4)

ABSTRACT

A process for the preparation of 2,2-bis-hydroxymethyl-butanediol-(1,4) of formula I ##STR1## wherein 4-hydroxybutyraldehyde of formula II ##STR2## and/or 2-hydroxytetrahydrofuran of formula III ##STR3## is/are condensed with formaldehyde in the presence of a basic catalyst and the resulting reaction mixture is then catalytically hydrogenated, and 2,2-bis-hydroxymethyl-butanediol-(1,4) is isolated from the hydrogenation product.

The present invention relates to a process for the preparation of2,2-bis-hydroxymethyl-butanediol-(1,4) of formula I ##STR4##

According to J. Org. Chem. 24, 1005 (1959), the co-aldolization of4-hydroxybutyraldehyde with formaldehyde with batchwise hydrogenation ofthe resulting crude 2,2-bis-hydroxymethyl-butyraldehyde with Raneynickel yields a viscous syrup, from which2,2-bis-hydroxymethyl-butanediol-(1,4) cannot be isolated byconventional separation techniques. To obtain compound I, it isnecessary to acetylize the resulting hydrogenation mixture with aceticanhydride to form the tetraacetic acid ester, which can be isolated andconverted to compound I by transesterification with methanol. Using thismethod, it is only possible to synthesize2,2-bis-hydroxymethyl-butanediol-(1,4) (I), referred to below as BHB, inan overall yield of 24%, based on 4-hydroxybutyraldehyde. This highlyunsatisfactory yield and the very laborious and costly method used forthe isolation of the target product makes this process unsuitable forindustrial applications.

The low yields are possibly due to side reactions occurring between theintermediate products 4-hydroxy-2-hydroxymethyl-butyraldehyde and2,2-bis-hydroxymethyl-butyraldehyde, such as dehydrations,retro-aldolizations, and polymerizations, but such a possibility has notbeen subjected to close examination.

EP-A 340,970 reveals that the reaction of 4-hydroxybutyraldehyde withformaldehyde under hydrogenating conditions produces virtually only2-methylbutanediol-(1,4) and 1,4-butanediol. BHB is apparently notformed under these conditions.

It is thus an object of the invention to provide a process for theeconomical preparation of BHB.

Accordingly, we have found a process for the preparation of2,2-bis-hydroxymethyl-butanediol-(1,4) of formula I ##STR5## wherein4-hydroxybutyraldehyde of formula II ##STR6## and/or2-hydroxytetrahydrofuran of formula III ##STR7## is/are condensed withformaldehyde in the presence of a basic catalyst and the resultingreaction mixture is then catalytically hydrogenated, and2,2-bis-hydroxymethyl-butanediol-(1,4) is isolated from thehydrogenation product.

The chemical reactions forming the basis of the process of the inventionare illustrated by the following reaction schemes: ##STR8##4-Hydroxybutyraldehyde II, in equilibrium with its cyclic half-acetal2-hydroxytetrahydrofuran III, is condensed in an aldolization with 2molecules of formaldehyde to form 2,2-bis-hydroxymethyl-butyraldehydeIV, which is then hydrogenated to BHB.

To effect the aldolization, the formaldehyde is reacted with the4-hydroxybutyraldehyde II generally in a molar ratio of from 1.5:1 to3.0:1 and preferably from 1.8:1 to 2.5:1. The formaldehyde isadvantageously used in the form of an aqueous solution, in which theconcentration of formaldehyde can be, advantageously, from 10 to 50 wt%.

Suitable basic catalysts for use in the aldolization of the formaldehydewith 4-hydroxbutyraldehyde are, basically, all of such bases as arecommonly used for catalyzing aldol condensations, for example thehydroxides and carbonates of alkali metals and alkaline earth metals,tertiary amines and basic ion exchangers, but in the process of theinvention particular preference is given to tertiary amines, especiallytertiary alkylamines.

The tertiary amines used as catalysts in the process of the inventionmay be aliphatic, cycloaliphatic, or heterocycloaliphatic tertiaryamines. It is advantageous to use tertiary amines which contain from 3to 20 carbon atoms and preferably from 3 to 15 carbon atoms.Particularly preferred tertiary amines are those which are made up of C₁-C₄ alkyl groups. The following tertiary amines are mentioned by way ofexample: trimethylamine, triethylamine, tri-n-propylamine,tri-n-butylamine, triisopropylamine, triisobutylamine,methyldiethylamine, methyldiisopropylamine, ethyldiisopropylamine,dimethyl-tert-butylamine, N,N'-tetramethyl-ethylenediamine,N,N',N"-pentamethyl-ethylenetriamine, cyclohexyl-dimethylamine,dicyclohexyl-methylamine, tribenzylamine, benzyldimethylamine,N-methylpyrrolidine, N-methylpiperidine, N,N'-dimethylpiperazine,N,N'-diethylpiperazine, N-methylmorpholine, triethanolamine,methyldiethanolamine, quinuclidine, and 1,4-diazabicyclo[2.2.2]octane.

The base is usually used in a concentration of from 0.5 to 25 mol % andpreferably from 1.0 to 10 mol %, based on the 4-hydroxybutyraldehyde.

The condensation of the 4-hydroxybutyraldehyde with formaldehyde isgenerally carried out at a temperature of from 0° to 100° C. andpreferably from 1° to 70° C. and more preferably from 1° to 40° C. Thereaction is advantageously carried out at atmospheric pressure. It isalso possible to operate under pressure, preferably the autogenouspressure of the reaction system, or under reduced pressure.

The aldol condensation is normally carried out in an aqueous reactionmedium, but there may be added, if desired, other, organic solventswhich are inert under the reaction conditions and which are preferablyreadily miscible with water, such as tetrahydrofuran, dioxane, anddimethoxyethane.

On completion of the aldol condensation and prior to the hydrogenation,the basic catalyst may, if desired, be neutralized by the addition of anacid, and it is preferred that neutralization be effected by the use ofan acidic ion exchanger, which can be easily removed from the reactionmixture by mechanical separation, e.g., filtration or centrifugation.This technique is particularly useful when inorganic catalysts are used.If distillable basic catalysts, such as tertiary amines, are used forthe aldol condensation, they can be removed from the reaction mixture,if desired, by distillation. Alternatively, the following hydrogenationstage can be carried out in the presence of such basic catalysts. Inparticular, in the preferred embodiment of the process of the invention,i.e., when a tertiary amine is used as the aldol condensation catalyst,the hydrogenation of the aldolization product may be carried out insitu, i.e., without previously separating the catalyst.

For the hydrogenation, the 2,2-is-hydroxymethylbutyraldehyde IV isadvantageously used in a solution having a content of IV of not morethan 50 wt %. Prior to the hydrogenation, it is therefore advantageousto add a further quantity of solvent to the reaction mixture coming fromthe aldol condensation. It is particularly preferred to dilute saidreaction mixture with water such that the solution to be hydrogenatedhas a water content of, usually, from 50 to 90 wt % and preferably from70 to 85 wt %.

Alternatively, an organic solvent may be added to the reaction mixturecoming from the aldol condensation instead of water, which solvent mustbe inert under the conditions of hydrogenation and is preferably onewhich is readily miscible with the water already present in the reactionmixture.

Examples of suitable solvents are ethers such as tetrahydrofuran,dioxane, and dimethoxyethane, C₁ -C₄ alcohols, in particular methanol,ethanol, propanol, and isopropanol, ethylene glycol, methoxyethanol, andethoxyethanol.

A further possibility is to remove all or some of the water from thereaction mixture to be hydrogenated, for example by distillation, andthen to replace it completely or partially by an organic solvent. If allor most of the water is removed from the reaction mixture, it can bereplaced by an organic solvent which is immiscible or less readilymiscible with water. In the case of the use or co-use of organicsolvent, it is advantageous to add this to the reaction mixture to behydrogenated in such quantity that the total concentration of waterand/or organic solvent in the reaction mixture to be hydrogenated isfrom 50 to 90 wt % and preferably from 70 to 85 wt %.

The hydrogenation of the resulting solution containing the aldolcondensation product, 2,2-bis-hydroxymethyl-4-hydroxybutyraldehyde, canbe carried out in conventional manner at temperatures generally rangingfrom 70° to 200° C. and under a pressure of, usually, from 1 to 200 bar.Hydrogenation is preferably carried out using a heterogeneous catalyst.This hydrogenation catalyst can be suspended in the reaction mixture ortake the form of a fixed bed. The mixture to be hydrogenated can bepassed upwardly through the fixed bed or allowed to trickle downwardlythrough the fixed bed. The residence times used are generally from 10 to300 min and preferably from 20 to 120 min.

To effect hydrogenation of 2,2-bis-hydroxymethyl-4-hydroxybutyraldehydeto BHB it is possible to use basically any of the conventionalhydrogenation catalysts, for example catalysts containing nickel,cobalt, copper, manganese, molybdenum, rhenium and/or the platinummetals palladium, platinum, and ruthenium. It is possible to use thepure metals, finely divided or in the form of nets or other structuresof large surface area, or catalysts containing a plurality of thesemetals. The hydrogenation catalysts may be used in the form of solidcatalysts or supported catalysts. In the latter case conventionalsupport materials may be used, for example silicon dioxide, aluminumoxides, zirconium dioxide, titanium dioxides, activated charcoal, bariumsulfate, barium carbonate, calcium carbonate and the like. Reference ismade, by way of example, to the hydrogenation catalysts taught in R. L.Augustine, Catalytic Hydrogenation, Chapter 3, Marcel Dekker, Inc., NewYork 1965, EP-A 335,222, DE-A 1,257,753, U.S. Pat. No. 3,449,445, DE-A2,321,101, EP-A 44,444, and DE-A 3,904,083. It is preferred to use, inthe process of the invention, catalysts containing copper and/or cobaltand/or ruthenium catalysts, especially ruthenium on alumina.Particularly preferred copper- and/or cobalt-containing catalysts arethe catalysts disclosed in DE-A 2,321,101, EP-A 44,444, and DE-A3,904,083.

Both the aldol condensation and the hydrogenation can be carried outbatchwise or continuously in conventional reactors.

The desired product BHB can be isolated from the hydrogenation mixturein a simple manner by conventional methods, for example by theextraction of an aqueous hydrogenation solution by means of an organicsolvent which is sparingly soluble in water, examples being sparinglysoluble alcohols, ketones, ethers, esters, and halogenated hydrocarbons,or by crystallization. The BHB is preferably purified and isolated bydistillation. During distillation, the tertiary amine which may havebeen used as catalyst can be recovered and, if desired, recycled to thealdol condensation stage.

The target product BHB is produced by the process of the inventioneconomically and in good yields and high purity.

BHB has many applications. For example it can be used in the manufactureof alkyd resins and coatings, as the polyol component in the manufactureof polyurethanes, and in the manufacture of plasticizers andemulsifiers.

The 4-hydroxybutyraldehyde used for the synthesis thereof can beobtained as proposed in EP-A 293,818 by isomerization of2-butenediol-(1,4) or alternatively via the hydroformylation of allylalcohol, as described in EP-A 150,943.

EXAMPLES Example 1

176 g (2 mol) of 4-hydroxybutyraldehyde, 500 g of 30 wt % formalin (5mol of formaldehyde) and 3 g (0.03 mol) of triethylamine were mixedtogether and stirred for 1 h at 25° C. and then for 1 h at 40° C. Thereaction mixture was then diluted with 1000 g of water, and theresulting solution was continuously hydrogenated at a temperature of130° C. and a pressure of 90 bar. The hydrogenation catalyst used was acopper on alumina catalyst as described in EP-A 44,444, in which thecopper content (calculated as CuO) was 55 wt % and the alumina content(calculated as Al₂ O₃) was 44.5 wt %. The throughput was 1.2 L ofsolution per liter of catalyst per hour. The hydrogenation product wasworked up by distillation to give 201 g of BHB (bp 200°-205° C./1 torr;mp 87° -88° C.) corresponding to a yield of 67% based on4-hydroxybutyraldehyde used.

Example 2

The aldol condensation was carried out as described in Example 1.Substantially all of the water present in the reaction mixture was thendistilled off under reduced pressure (3 mbar, temperature at bottom ofstill: 50° C.), and the residues were dissolved in three times theirweight of tetrahydrofuran. The resulting solution was continuouslyhydrogenated at a temperature of 170° C. and a pressure of 90 bar. Thehydrogenation catalyst used was a catalyst as described in DE-A3,904,083 and containing 66.8 wt % of cobalt (calculated as CoO), 19.1wt % of copper (calculated as CuO), 7.1 wt % of manganese (calculated asMn₂ O₃), 3.3 wt % of molybdenum (calculated as MoO₃), 3.5 wt % ofphosphoric acid (calculated as H₃ PO₄), and 0.15 wt % of sodium(calculated as Na₂ O). The throughput through the catalyst was 1.9L/(L·h). Following purification of the hydrogenation product bydistillation, BHB was obtained in a total yield of 54% based on4-hydroxybutyraldehyde used.

We claim:
 1. A process for the preparation of2,2-bis-hydroxymethyl-butanediol-(1,4) of formula I ##STR9## whichcomprises: condensing 4-hydroxybutyraldehyde of formula II ##STR10##and/or 2-hydroxytetrahydrofuran of formula III ##STR11## withformaldehyde in the presence of a basic catalyst at a temperature offrom 0° to 100° C. catalytically hydrogenating the resulting reactionmixture at a temperature of from 70° to 200° C. and a pressure of from 1to 200 bar and isolating 2,2-bis-hydroxymethyl-butanediol-(1,4) from thehydrogenation product.
 2. The process of claim 1, wherein the basiccatalyst used is a tertiary amine.
 3. The process of claim 1, whereinthe hydrogenation is carried out in an organic solvent or a mixture oforganic solvent and water.
 4. The process of claim 1, wherein thereaction mixture to be hydrogenated has a water content of from 50 to 90wt %.
 5. The process of claim 1, wherein the hydrogenation is carriedout over a heterogeneous hydrogenation catalyst in the presence ofhydrogen.
 6. The process of claim 1, wherein the condensation reactiontakes place at a temperature of from 1° to 70° C.